1. Field of Invention
The present invention relates generally to handrail drive apparatuses, and more particularly, to linear handrail drive apparatuses typically used in conjunction with moving walkways, travelators, escalators, and the like.
2. Discussion of Related Art
Linear handrail drives have existed for many years. Such handrail drives were developed to elevate handrails entirely above the step band of a moving walkway and/or escalator and thereby avoid routing the handrail down into the truss to be driven directly by the same elements arranged to drive the step band. Notwithstanding the advantages that arise from this configuration, known linear handrail drives have been fraught with problems such as difficulty in effecting adjustment, lack of reliability, capacity limitations, the inability to incorporate special handrails, and relatively rapid deterioration.
FIG. 1A depicts one example of a traditional linear handrail drive apparatus 10. The handrail drive apparatus 10 includes a plurality of driving wheel members 12 arranged to drive a handrail 14. Each of the driving wheel members 12 includes an input portion 12a and an output portion 12b. The input portions 12a of each of the driving wheel members 12 are connected with one another via a connecting member 16 such as, for example, a chain or belt or the like. A drive motor 18 is coupled to the input portion 12a of at least one of the driving wheel members 12 via an input connecting member 16a. The handrail 14 is forced against the output portion 12b of each driving wheel member 12 by a respective pinch roller 20 positioned on an opposite side of the handrail 14. In operation, the drive motor 18 drives one of the driving wheel members 12 which, in turn, drives another driving wheel member 12 via connecting member 16 at substantially the same angular velocity. As a result, the output portions 12b of each driving wheel member 12 drive the handrail 14 to move. When the structural attributes of all of the foregoing members in the handrail drive apparatus 10 are equal (e.g., the diameter and hardness of each of the driving wheel members 12 are equal; the pinch force applied to the handrail 14 by each pinch roller 20 is equal), and the angular velocities of members 12 are equal, the linear velocity of the output portion 12b of each driving wheel member 12 will also be equal. Consequently, the linear velocity imparted to the handrail 14 by each of the driving wheel members 12 is equal since the rolling radii of the driving wheel members 12 are equal.
Generally, however, the respective driving wheel members 12 are not equal in all respects due to various differences and defects inherent in standard manufacturing processes. For example, the output portion 12b of one or more driving wheel members 12 may not be completely round or may have a diameter that differs slightly from one or more of the other driving wheel members 12. As another example, one or more driving wheel members 12 may have different hardnesses and/or the pinch force applied to the handrail 14 by each respective pinch roller 20 may not be consistent. Any of the foregoing differences can effectively create differing rolling radii in each of the driving wheel members 12. As shown in FIG. 1A, for example, the rolling radii of the respective output portions 12b of the driving wheel members 12 may not be equal to one another and, as a result, the output portion 12b having the smaller radius will attempt to drive the handrail 14 at a slower linear velocity than the output portion 12b having the larger radius. Where the driving wheel members 12 attempt to drive the handrail 14 at different linear velocities, slipping or scrubbing of some or all of the driving wheel members 12 against the handrail 14 must occur for the handrail 14 to move. As one of ordinary skill in the art will recognize, operation involving slipping/scrubbing introduces inefficiencies related to dynamic friction coefficients, whereas operation under pure rolling conditions takes advantage of more efficient static friction coefficients. The end result is an inefficient drive apparatus with high wear, increased debris generation, and reduced capacity due to imperfect operating conditions.
One attempt to alleviate the inefficiencies in traditional linear handrail drives is depicted in FIG. 1B, which shows a linear handrail drive apparatus 22 including a handrail 23, a drive motor 24, an input connecting member 26, a primary driving wheel member 28, at least one secondary driving wheel member 32, a connecting member 30, and a plurality of pinch rollers 34. The drive motor 24 is drivably coupled to an input portion 28a of the primary driving wheel member 28 via the input connecting member 26 which may be, for example, a chain or belt or the like. An output portion 28b of the primary driving wheel member 28 is coupled to the at least one secondary driving wheel members 32 via a connecting member 30 which may be, for example, a chain, a poly vee or cogged belt configured to engage the handrail 23. The plurality of pinch rollers 34 are positioned opposite the primary and secondary driving wheel members 32 to force contact between the handrail 23 and connecting member 30 and thereby impart motion to the handrail 23. While this configuration offers some improvement to the above-described inefficiencies associated with traditional linear handrail drives, it also has inherent shortcomings. For example, since the linear stiffness of the connecting member 30 is typically far less than the linear stiffness of the handrail 23, the majority of driving force imparted to the handrail 23 occurs at the first pinch location (i.e., at the primary driving wheel member 28) since the driving force at downstream pinch locations is limited by the small stretch of the handrail 23 compared to the required stretch of the connecting member 30 between pinch locations to assume load. Thus, most of the load is taken on by the connecting member 30 and primary driving wheel member 28 at the first pinch location as long as, or until, the connecting member 30 becomes unable to drive the handrail 23 by itself at the first pinch location, at which time the handrail 23 slips relative to the connecting member 30, allowing stretch of the connecting member 30 and, in turn, allowing load to be transferred to the next pinch location (i.e., at the adjacent secondary driving wheel member 32). This slipping and loading cascade continues until equilibrium occurs and the handrail 23 is in motion. Thus, as long as the connecting member 30 is not able to drive the handrail 23 by itself at the first pinch location, small but continuous slipping occurs at sequential pinch locations depending on the driving force/load requirements of the handrail 23. The result is much the same as the aforementioned traditional linear handrail drives in that the apparatus causes wear of the handrail and connecting member, debris generation, and has diminished capacity due to slipping (dynamic friction coefficients) existing at most of the pinch locations.